Biomarkers are incorporated into cross-sectional, case-control and prospective cohort studies of occupational causes of cancer in order to enhance exposure assessment, provide insight into early biologic effects of specific chemicals, evaluate sources of genetic susceptibility and classify tumors at the molecular level to identify subgroups that may be more etiologically homogenous. A cross-sectional study of healthy workers exposed to benzene in Shanghai, China showed that exposed workers had elevated levels of chromosomal aberrations in peripheral lymphocytes, similar to the type observed in patients with chemically associated leukemias, and elevated levels of benzene oxide-albumin and hemoglobin adducts. A pilot study of pesticide applicators exposed to 2,4-D found that the lymphocyte replicative index was elevated in post-exposure compared with pre-exposure blood samples. A study of U.S. army soldiers deployed to Kuwait close to oil well fires in the aftermath of the Gulf War showed that various biomarkers of PAH exposure were not elevated during deployment compared to pre- and post-deployment samples collected while soldiers were stationed in Germany. Newly developed and on-going case-control studies of stomach, esophagus, brain, bladder and breast cancer, NHL, and benzene-induced hematotoxicity and hematologic malignancies and cohort studies of women in China and agricultural workers in the United States are evaluating a range of potential genetic risk factors and their interaction with occupational and environmental exposures. Most of these studies are also collecting tumor samples for future molecular analyses. In a study using the tumor tissue of 106 life-time nonsmoking women with lung cancer a signifcant gene-environment interaction was found between the GSTM-1 (Null) geneotype and environmental tobacco smoke.